1. Field
Aspects of the present disclosure relate generally to wireless communication systems, and more particularly, to establishing and maintaining high frequency communications in a wireless network.
2. Background
Wireless communication networks are widely deployed to provide various communication services such as voice, video, packet data, messaging, broadcast, and the like. These wireless networks may be multiple-access networks capable of supporting multiple users by sharing the available network resources. Such networks, which are usually multiple access networks, support communications for multiple users by sharing the available network resources. One example of such a network is the Universal Terrestrial Radio Access Network (UTRAN). The UTRAN is the radio access network (RAN) defined as a part of the Universal Mobile Telecommunications System (UMTS), a third generation (3G) mobile phone technology supported by the 3rd Generation Partnership Project (3GPP). Examples of multiple-access network formats include Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA) networks, and Single-Carrier FDMA (SC-FDMA) networks.
A wireless communication network may include a number of base stations or node Bs that can support communication for a number of user equipments (UEs). A UE may communicate with a base station via downlink and uplink. The downlink (or forward link) refers to the communication link from the base station to the UE, and the uplink (or reverse link) refers to the communication link from the UE to the base station.
A base station may transmit data and control information on the downlink to a UE and/or may receive data and control information on the uplink from the UE. On the downlink, a transmission from the base station may encounter interference due to transmissions from neighbor base stations or from other wireless radio frequency (RF) transmitters. On the uplink, a transmission from the UE may encounter interference from uplink transmissions of other UEs communicating with the neighbor base stations or from other wireless RF transmitters. This interference may degrade performance on both the downlink and uplink.
As the demand for mobile broadband access continues to increase, the possibilities of interference and congested networks grows with more UEs accessing the long-range wireless communication networks and more short-range wireless systems being deployed in communities. Research and development continue to advance the UMTS technologies not only to meet the growing demand for mobile broadband access, but to advance and enhance the user experience with mobile communications.
In general, wireless communications networks implement the aforementioned uplink and downlink communications between base stations and UEs using a low frequency carrier signal (e.g. 400 MHz-3 GHz). For example, current 3G networks utilize 850, 1700, 1900 and 2100 MHz frequencies and current 4G technologies utilize 700, 800, 1700, 1900, 2100 and 2500 MHz frequencies. Low frequency carrier signals provide certain advantages which have assisted with the widespread deployment of wireless networks. Such frequencies provide for a balance of coverage area range capabilities and the ability to handle a large number of UEs.
It is generally understood that the higher the frequency utilized, the smaller the available coverage area becomes. This is true even within the range of low frequency networks (e.g. 1900 MHz transmissions generally do not cover as much distance as an 800 MHz transmission). Further, it is understood that use of the higher end of the low frequency range, such as 1900 MHz, allows for higher bandwidth and the ability to provide service to more UEs.
Wireless communication networks generally do not utilize frequencies in a much higher range, e.g. 20 GHz-60 GHz because such high frequency signals would suffer multiple drawbacks if they were to be deployed in a wireless communication network setting. For example, at a frequency of 28 GHz, the free space path loss of a signal is 20 dB larger than a 2 GHz signal. Oxygen absorption and other atmospheric conditions (e.g. presence of rain, water vapor and the like) also impact high frequency signals more adversely. Penetration loss is also much larger at high frequencies when a signal encounters buildings, foliage, etc. Because of this, high frequency communications are not utilized in typical wireless communications networks.
Further, communication at high frequencies often requires line of sight (LOS) connections. This raises multiple technical challenges for initially aligning a beam which facilitates a connection and maintaining communications between a base station and a UE, especially in an environment where the UE is mobile. For example, current beam scanning methods, e.g. utilized in IEEE 802.15.3c, require successive scans and beam refinements using layered training and feedback techniques. The successive scans eventually lead to a beam alignment between a base station and a UE, but such an alignment takes a considerable amount of time. Additionally, these methods are limited in the types of environments that may be utilized. For example, such beam scanning is usually only implemented in short range indoor systems with reasonable signal to noise ratio properties and will also usually allow for wide beams.